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--- evn:evn_science [2018/09/12 09:24] – [Gravitationally-lensed radio arcs observed with global VLBI] antonis
+++ evn:evn_science [2018/09/12 09:34] – [A dust-enshrouded tidal disruption event with a resolved radio jet in a galaxy merger] antonis
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 An international team of astronomers have, for the first time, directly imaged the formation and expansion of a fast-moving jet of material ejected when the powerful gravity of the SMBH in the nucleus of Arp 299-B (D=45 Mpc) ripped apart a star that wandered too close to the cosmic monster in Arp 299-B. It is one of the two merging galaxies (Arp 299-A and Arp 299-B) forming the Arp 299 system, which hosts prolific supernova factories in its nuclear regions.
 The team tracked the event with radio and infrared telescopes, including the EVN, for over a decade. The patient, continued observations with the EVN and other radio telescopes around the world, eventually showed the source of radio emission expanding in one direction, just as expected for a jet (Fig. 2). The measured expansion indicated that the material in the jet moved at an average of about one-fourth the speed of light. The crucial piece of information solving the puzzle of this event was provided by VLBI observations, as the inferred angle of the jet to the line-of-sight was in clear disagreement with expectations from a "normal" AGN jet, while in the case of a TDE this angle can have any value.
+{{ :evn:arp299_transient_science2018.jpg?400 |}}
+**Figure:** The tidal disruption event Arp 299-B AT1 and its expanding radio jet. (A) A color-composite optical image from the HST, with high-resolution, near-IR 2.2 micron images [insets (B) and (C)] showing the brightening of the B1 nucleus. (D) Radio evolution of Arp 299-B AT1 as imaged with VLBI at 8.4 GHz [7×7 mas region with the 8.4-GHz peak position in 2005, RA= 11h28m30.9875529s, dec= 58°33ʹ40ʹʹ.783601 (J2000.0), indicated by the dotted lines]. The VLBI images are aligned with an astrometric precision better than 50 mas. The initially unresolved radio source develops into a resolved jet structure a few years a_er the explosion, with the centre of the radio emission moving westward with time at an average intrinsic speed of 0.22 >mes the speed of light. The radio beam size for each epoch is indicated in the lower-right corner.
 The gravitational field of the SMBH in Arp 299-B, with a mass 20 million Tmes that of the Sun, shredded a star with a mass more than twice that of the Sun. This resulted in a TDE that was not seen in the optical or X-rays because of the very dense medium surrounding the SMBH, but was detected in the near-infrared and radio. The so| X-ray photons produced by the event were efficiently reprocessed into UV and optical photons by the dense gas, and further to infrared wavelengths by dust in the nuclear environment. Efficient reprocessing of the energy might thus resolve the outstanding problem of observed luminosities of optically detected TDEs being generally lower than predicted.
 The case of Arp 299-B AT1 suggests that recently formed massive stars are being accreted onto the SMBH in such environments, resulting in TDEs injecting large amounts of energy into their surroundings. However, events similar to Arp 299-B AT1 would have remained hidden within dusty and dense environments, and would thus not be detectable by optical, UV or so| X-ray observations. Such TDEs from relatively massive, newly formed stars might provide a large radiative feedback, especially at higher redshifts where galaxy mergers and luminous infrared galaxies like Arp 299 are more common.
-Published in: Makla S., Perez-Torres M., et al.: A dust enshrouded tidal disruption event with a resolved radio jet in a galaxy merger. Science, 2018
+Published in: Makla S., Perez-Torres M., et al.: A dust enshrouded tidal disruption event with a resolved radio jet in a galaxy merger. [[http://science.sciencemag.org/content/early/2018/06/13/science.aao4669|Science, 2018]]